1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a method and apparatus for processing video data of the liquid crystal display device capable of preventing a video quality from being deteriorated by an overdriven action (hereinafter referred to as an overdriving action).
2. Discussion of the Related Art
A liquid crystal display (LCD) device displays video or video data using electrical and optical characteristics of a liquid crystal. In more detail, the liquid crystal display (LCD) device includes a liquid crystal panel for displaying video or video data through a pixel matrix and a driving circuit for driving the liquid crystal panel. Since the LCD device is a non-emissive element, the LCD device includes a backlight unit for emitting light at a backside of the liquid crystal panel. The liquid crystal panel changes a liquid-crystal alignment status of respective sub-pixels according to video signals, adjusts a transmission rate of the light emitted from the backlight unit, such that it displays video or video data thereon. This LCD device has been widely used to various displays from small-sized displays to large-sized displays, for example, mobile communication terminals, mobile computers, LCD TVs, etc.
The LCD display has a structure of an active matrix type, each sub-pixel of which includes a thin film transistor (TFT) used as a switching element. However, due to not only a slow response speed caused by unique viscosity and elasticity of the liquid crystal, but also hold-type driving characteristics, a motion blur effect caused by an afterimage (i.e., image retention) of a previous frame unavoidably occurs when moving videos or motion pictures are reproduced.
For example, as shown in FIG. 1A, if a data voltage applied to a liquid crystal at an n-th frame (Fn) is changed, a luminance or brightness is not directly changed to a target gray level, but is slowly changed from a gray level of a previous frame (Fn−1) to the target gray level, such that the changed result unavoidably affects even the next frame (Fn+1), resulting in the occurrence of an afterimage. In order to solve the above-mentioned problem, an overshoot voltage higher than a target voltage is applied at a data changing moment, such that an overdriving method for improving a liquid crystal response speed in proportion to the applied voltage has been widely used. This overdriving method compares data of a previous frame with data of a current frame. If a difference in data between the previous frame and the current frame is equal to or higher than 1, the data of the current frame is changed to overdriving data such that the overdriving data is outputted.
In the meantime, a quantization error of more than one gray level (i.e., 1 gray level) may occur in a quantization process for sampling analog broadcast signals received from a television (TV) to digital data. Therefore, although the analog broadcast signal corresponds to a still image, individual frames may output different digital data due to the quantization error. However, components of the quantization error are amplified by an overdriving circuit during a data processing step of the LCD device, such that they appear as noise on the screen.
Also, if overdriving circuit of the related art independently changes red (R), green (G), and blue (B) data to overdriving data and increases overdriving components to make a faster response speed, color inversion occurs, resulting in deterioration of an video quality.